Four bodies were found by police Wednesday in Nezahaulcoyotl, a city in Mexico state, which surrounds the Federal District and forms part of the Mexico City metropolitan area, officials said.
Officers found the victims after receiving a tip from residents, a spokesman for the Public Safety Secretariat told Efe.
Three of the victims were pronounced dead at the scene and the fourth died at La Perla Hospital.
The four people were shot in the early morning hours between Corrido del Norte and Morenita streets, where the bodies were found.
A message supposedly written by the La Familia Michoacana drug cartel was left with the bodies, but the content is not known, media reports said.
The unidentified victims are believed to be in their 30s and 40s.
Investigators found about 20 bullet casings at the crime scene, media reports said.
La Familia Michoacana, which operates in the western state of Michoacan, the southern state of Guerrero and the central state of Mexico, has been badly weakened by the arrests and killings of several of its top leaders, and the creation of the Los Caballeros Templarios gang.
La Familia was considered the largest trafficker of synthetic drugs in Mexico at one time.
Los Caballeros Templarios, which was founded in March 2011 by former La Familia members, deals in both synthetic drugs and natural drugs. EFE